I know there are those uneducated in breastfeeding that may occasionally do something stupid like ask us to leave, but for the most part we can put more pressure on ourselves. When you nurse in public, you educate and encourage other moms, So thank you for nursing in public! The more you do, the more it is widely accepted and those moms who are hindered from breastfeeding because "I have never seen it done." will no longer be hindered.
To cover or not to cover is up to you, but the right top can provide you the modesty you want without being under a blanket. If you are near other moms, they benefit from seeing you nurse. If an uneducated person approaches, look them in the eye. Their eyes will ususally follow yours. And if they have the audacity too ask you to leave, have a retort ready like you really don't want hundreds of my pro-breastfeeding friends organizing a nurse-in at your business, do you?